Field of the Invention:
This invention relates to a temperature sensing means such as a thermostat useful for generating analog voltage error signals about a plurality of set temperature points and for developing conditioned command signals therefrom which are useful in control circuits of an air conditioning system.
Brief Statement of the Prior Art:
Air conditioning systems for providing one or more zones of controlled air temperatures within a building have commonly employed a single thermostat in each of the controlled zones of the building. These thermostats are operative to activate heating or cooling means of the air conditioning system in response to the deviation of the control zone temperature below or above a single, set temperature point. The thermostats have included circuits for developing analog DC voltage command signals by the employment of thermistors with negative temperature coefficients in the manner described in U.S. Pat. No. 3,702,431.
The increasing concern with energy consumption in the air conditioning of buildings has lead to the suggestion that the cooling facilities be controlled by a high set temperature point, typically about 78.degree. F. and the heating facilities be controlled at a lower set temperature point, typically about 68.degree. F. The application of existing thermostats to such systems does not provide adequate control over the fixed adjustability of the set temperature points.
A number of fairly complex, solid state circuits have been devised for developing a command signal from a thermostat such as described in the aforementioned patent. A common failing of these devices is the absence of any protective circuit means whereby the delicate circuit components can be protected in the event that the output terminals of the circuit are inadvertently grounded across its voltage supply.